These implants must meet several criteria to ensure good stability between two vertebral bodies while allowing a satisfactory fusion rate to be guaranteed. To do this, the implant body which is inserted under pressure between the vertebral bodies must have very high strength along the axis of the vertebral column on the one hand, and a large area of contact with the adjacent vertebral bodies and the residual elements of the vertebral bodies on the other hand.
The implant must have a high mechanical strength relative to the stresses exerted by the vertebral bodies in order to maintain the intervertebral space. Generally speaking, in practice the implant must have a strength 2 to 3 times greater than the forces exerted by the vertebral bodies on the implant. The implant must be resistant at least until bone consolidation.
Generally speaking, the implant is a solid hollow body filled with bone grafts. The walls have openings to allow bone fusion with the vertebral bodies.
The implant is placed between two vertebral bodies, either horizontally in the direction of its thickness or vertically in the direction of its height.
The implant may be classified according to the shape of the body. It may be a parallelepiped of rectangular cross section. In order to adapt better to the shape of the vertebral bodies, it may be ogival or slightly rounded.
It is known for an implant to consist of a cylindrical or oval cage that is hollow inside in order to receive bone grafts, the wall of the cage comprising a set of openings. This type of implant enables a bone fusion around the implant and with the vertebral plates, the center of the grafts conversely not fusing or fusing only partially.
There are also implants comprising only two plates positioned at the ends of an axis. The surgeon is led to fill the implant with compacted grafts all around the axis once the implant is positioned between two vertebral bodies. This type of implant effectively offers a relatively large circumferential area of contact with the external surroundings. However, due to its shape it does not enable the grafts to be kept at the location of the area requiring a bone reconstruction. In addition, the insertion of the grafts into the implant lengthens the operation time.
It would therefore be advantageous for an implant to be available having a very strong structure while having a large and continuous area of contact with the outside for the bone fusion and an optimal holding shape so as to hold the bone grafts.